How to calculate the theoretical yield of aspirin to be obtained when 2.0 g of salicylic acid and 5.0 mL of acetic anhydride (density = 1.08 g/mL) are mixed together? ( Molar masses: acetic anhydride = 102.1 g/mol; salicylic acid = 138.2 g/mol)

Most of these stoichiometry problems are worked the same way. This problem is a limiting reagent problem and stoichiometry rolled into one.

1. Write and balance the equation.
2. Convert g salicylic acid to moles. Moles = grams/molar mass. Convert 5.0 mL acetic anhydride (using density) to grams, then to moles.
3a. Using the coefficients in the balanced equation, convert moles salicylic acid to moles aspirin.
3b. Using the same procedure, convert moles acetic anhydride to moles aspirin.
3c. Most likely you will get two different answers for 3a and 3b. Obviously, both can't be correct. The correct answer in these problems is ALWAYS the smaller value.
4. Using the smaller value found in 3c, convert moles to grams of product. grams = moles x molar mass.
The answer obtained is the theoretical yield.

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жНЙю

To calculate the theoretical yield of aspirin, you need to determine the limiting reactant, convert the mass of the limiting reactant to moles, and then use the stoichiometry of the balanced equation to calculate the moles of aspirin that can be produced. Finally, convert the moles of aspirin to grams.

Here's the step-by-step process:

Step 1: Determine the limiting reactant
The limiting reactant is the reactant that will be completely used up first and limits the amount of product that can be formed. You can calculate the moles of each reactant and compare them to determine the limiting reactant.

Moles of salicylic acid = mass of salicylic acid / molar mass of salicylic acid
Moles of salicylic acid = 2.0 g / 138.2 g/mol = 0.0144 mol

Moles of acetic anhydride = volume of acetic anhydride x density of acetic anhydride / molar mass of acetic anhydride
Moles of acetic anhydride = (5.0 mL x 1.08 g/mL) / 102.1 g/mol = 0.0511 mol

Comparing the moles, salicylic acid has fewer moles (0.0144 mol) compared to acetic anhydride (0.0511 mol). Therefore, salicylic acid is the limiting reactant.

Step 2: Calculate the moles of aspirin
The balanced chemical equation for the reaction between salicylic acid and acetic anhydride is:
Salicylic acid + Acetic anhydride → Aspirin + Acetic acid

According to the balanced equation, the stoichiometry is 1:1. This means that 1 mole of salicylic acid reacts with 1 mole of acetic anhydride to produce 1 mole of aspirin.

Since salicylic acid is the limiting reactant, the number of moles of aspirin formed will be equal to the moles of salicylic acid.

Moles of aspirin = moles of salicylic acid = 0.0144 mol

Step 3: Convert moles of aspirin to grams
To find the mass of aspirin formed, multiply the moles of aspirin by the molar mass of aspirin.

Mass of aspirin = moles of aspirin x molar mass of aspirin
Mass of aspirin = 0.0144 mol x 180.16 g/mol = 2.59 g

Therefore, the theoretical yield of aspirin that can be obtained is 2.59 grams.